The present invention relates to electroluminescent lighting fixtures for lighting the face or dial of an instrument. More particularly, the invention relates to electroluminescent lighting fixtures designed for use in military aircraft which are especially arranged for viewing compatibility with both the naked eye and with the night vision goggles of an aircraft pilot.
In providing lighting for an instrument, it is advantageous to provide low intensity light which uniformly lights the instrument and which does not produce undesirable reflections and glare. It is also advantageous to provide a fixture which is mechanically compatible with the instrument it is to light, especially where retrofitting is to be used to replace the previous light source or to add illumination to an instrument which previously was not lit. Various apparatus have been proposed and are presently being utilized in illuminating the faces (dials) of instruments on military aircraft. Most apparatus use incandescent lamps which provide light which is either non-compatible with night vision viewing, too great in intensity to be used with night vision goggles, or which is non-uniform when reduced in intensity. Also, when incandescent lighting is provided around the dial, undesirable reflections and glare result.
U.S. Pat. No. 4,328,532 to Richard A. Smith, discloses a light source which purportedly eliminates some of the difficulties of the prior art by providing a lighting fixture comprising a housing with a centrally disposed opening and an inner cylindrical wall, an electroluminescent lamp adjacent the wall, a microlouver light shield placed over the lamp to prevent viewing of the intense light and to eliminate reflections, and a polarizer placed between the lamp and the microlouver shield to polarize the light and reduce reflection and glare. According to the Smith, the described apparatus provides a uniform illumination of the face of the instrument and permits viewing through night vision goggles. However, because microlouver shields are commercially available with the louvers at only a couple of predetermined angles and because the microlouvers by their nature block out light, the Smith device does not provide the brightness and uniformity of illumination over the entire face of the instrument diel that is desired. Moreover, the Smith device is difficult and expensive to manufacture and assemble, is not configured to be mounted within an instrument enclosure, and is not necessarily easily attached to existing instruments.